
package nu.aing.algo;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.PriorityQueue;

/**
 * Source : http://www.algolist.com/code/java/Dijkstra%27s_algorithm
 * 
 * @author memekmaut@gmail.com
 */
public class DjikstraAlgorithm {

    public static void main(String[] args) {
        Vertex v0 = new Vertex("Redvile");
        Vertex v1 = new Vertex("Blueville");
        Vertex v2 = new Vertex("Greenville");
        Vertex v3 = new Vertex("Orangeville");
        Vertex v4 = new Vertex("Purpleville");

        v0.adjacencies = new Edge[] { new Edge(v1, 5),
                new Edge(v2, 10),
                new Edge(v3, 8) };
        v1.adjacencies = new Edge[] { new Edge(v0, 5),
                new Edge(v2, 3),
                new Edge(v4, 7) };
        v2.adjacencies = new Edge[] { new Edge(v0, 10),
                new Edge(v1, 3) };
        v3.adjacencies = new Edge[] { new Edge(v0, 8),
                new Edge(v4, 2) };
        v4.adjacencies = new Edge[] { new Edge(v1, 7),
                new Edge(v3, 2) };
        Vertex[] vertices = { v0, v1, v2, v3, v4 };
        Djikstra.computePaths(v0);
        for (Vertex v : vertices)
        {
            System.out.println("Distance to " + v + ": " + v.minDistance);
            List<Vertex> path = Djikstra.getShortestPathTo(v);
            System.out.println("Path: " + path);
        }
    }
}

class Djikstra {
    public static void computePaths(Vertex source)
    {
        source.minDistance = 0.;
        PriorityQueue<Vertex> vertexQueue = new PriorityQueue<Vertex>();
        vertexQueue.add(source);

        while (!vertexQueue.isEmpty()) {
            Vertex u = vertexQueue.poll();

            // Visit each edge exiting u
            for (Edge e : u.adjacencies)
            {
                Vertex v = e.target;
                double weight = e.weight;
                double distanceThroughU = u.minDistance + weight;
                if (distanceThroughU < v.minDistance) {
                    vertexQueue.remove(v);
                    v.minDistance = distanceThroughU;
                    v.previous = u;
                    vertexQueue.add(v);
                }
            }
        }
    }

    public static List<Vertex> getShortestPathTo(Vertex target)
    {
        List<Vertex> path = new ArrayList<Vertex>();
        for (Vertex vertex = target; vertex != null; vertex = vertex.previous)
            path.add(vertex);
        Collections.reverse(path);
        return path;
    }
}

class Vertex implements Comparable<Vertex>
{
    public final String name;
    public Edge[] adjacencies;
    public double minDistance = Double.POSITIVE_INFINITY;
    public Vertex previous;

    public Vertex(String argName) {
        name = argName;
    }

    public String toString() {
        return name;
    }

    public int compareTo(Vertex other)
    {
        return Double.compare(minDistance, other.minDistance);
    }
}

class Edge
{
    public final Vertex target;
    public final double weight;

    public Edge(Vertex argTarget, double argWeight)
    {
        target = argTarget;
        weight = argWeight;
    }
}
